The diverse fauna and flora of rocky intertidal ecosystems are being impacted by the activities of rapidly increasing coastal populations in many regions of the world. Human harvesting of intertidal species can lead to significant changes in body sizes of these taxa. However, little is known about the temporal trajectories of such size declines and more importantly, the long-term effects of chronic human impacts. Furthermore, it is unclear whether sizes of species not directly targeted for harvesting are also declining through indirect effects. Here we use historical (extending back to 1869) and field survey data covering 200 km of mainland southern California coast to show that human activities have led to significant and widespread declines in body sizes of rocky intertidal gastropod species over the last century. These declines, initiated several decades ago, are continuing and contrary to expectation, they are not restricted to species harvested for human consumption. Data from the only national park in this area, where conservation laws are strictly imposed, demonstrate that negative ecological impacts can be ameliorated if existing laws are enforced.

Disease outbreaks can have substantial impacts on wild populations, but the often patchy or anecdotal evidence of these impacts impedes our ability to understand outbreak dynamics. Recently however, a severe disease outbreak occurred in a group of very well-studied organisms–sea stars along the west coast of North America. We analyzed nearly two decades of data from a coordinated monitoring effort at 88 sites ranging from southern British Columbia to San Diego, California along with 2 sites near Sitka, Alaska to better understand the effects of sea star wasting disease (SSWD) on the keystone intertidal predator, Pisaster ochraceus. Quantitative surveys revealed unprecedented declines of P. ochraceus in 2014 and 2015 across nearly the entire geographic range of the species. The intensity of the impact of SSWD was not uniform across the affected area, with proportionally greater population declines in the southern regions relative to the north. The degree of population decline was unrelated to pre-outbreak P. ochraceus density, although these factors have been linked in other well-documented disease events. While elevated seawater temperatures were not broadly linked to the initial emergence of SSWD, anomalously high seawater temperatures in 2014 and 2015 might have exacerbated the disease’s impact. Both before and after the onset of the SSWD outbreak, we documented higher recruitment of P. ochraceus in the north than in the south, and while some juveniles are surviving (as evidenced by transition of recruitment pulses to larger size classes), post-SSWD survivorship is lower than during pre-SSWD periods. In hindsight, our data suggest that the SSWD event defied prediction based on two factors found to be important in other marine disease events, sea water temperature and population density, and illustrate the importance of surveillance of natural populations as one element of an integrated approach to marine disease ecology. Low levels of SSWD-symptomatic sea stars are still present throughout the impacted range, thus the outlook for population recovery is uncertain.

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The pristine environmental conditions of offshore islands do not guarantee maximum genetic diversity. Future restoration and transplantation efforts of seagrasses must recognize cryptic species and consider the degree of both genetic and genotypic variation in candidate donor populations.

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We report the occurrence of the brown seaweed Sargassum filicinum Harvey in southern California.Sargassum filicinum is native to Japan and Korea. It is monoecious, a trait that increases its chance of establishment. In October 2003, Sargassum filicinum was collected in Long Beach Harbor. In April 2006, we discovered three populations of this species on the leeward west end of Santa Catalina Island. Many of the individuals were large, reproductive and senescent; a few were small, young but precociously reproductive. We compared the sequences of the mitochondrial cox3 gene for 6 individuals from the 3 sites at Catalina with 3 samples from 3 sites in the Seto Inland Sea, Japan region. The 9 sequences (469 bp in length) were identical. Sargassum filicinum may have been introduced through shipping to Long Beach; it may have spread to Catalina via pleasure boats from the mainland.